The major demographic shifts and aging of the population, as well as the rise in the costs of medical care make it imperative to understand the elderly's utilization patterns over time, the costs of services received, and the characteristics and medical problems of consistently high and low users. The provision of appropriate care, as well as cost effective interventions are dependent on such knowledge. Accordingly, the objectives of this study are: -To determine the consistency in patterns of ambulatory care utilization over an extended time among continuously enrolled elderly members of a large prepaid group practice HMO. -To determine the amount and types of medical care services and procedures utilized by consistently high and low elderly users. -To determine the relative values and dollar values (costs) of the services and procedures utilized by consistently high and low elderly users. -To identify and compare the high and low users' reasons for seeking care (i.e., symptoms, morbidities, and specific medical conditions). -To compare the high and low users with respect to the place of service and type of providers seen. -To identify the social, economic, and health characteristics which differentiate the consistently high and low elderly users. The proposed research overcomes the major difficulties of past research: utilization data derived from interviews, cross--ectional study designs, small non-representative samples, and short time frames. This study uses a longitudinal design which derives the utilization data from actual medical records and the independent predictor variables from carefully designed surveys.